1 Introduction

Vocabulary is one of the three elements of language and is the basis of all linguistic activities, it is impossible to express thoughts without vocabulary. Wilkins (1972) states that without grammar, only little can be expressed, but nothing can be expressed without vocabulary [1]. That's why vocabulary is so important.

Vocabulary learning has always been one of the main concerns of English teachers and learners, because limited vocabulary can hinder successful communication. Acquiring and using vocabulary is the foundation for improving language knowledge and developing language skills, the teaching effect of vocabulary is relevant to the realization of the goals of foreign language teaching. Learning a sufficient number of words in English is a difficult task for L2 learners.

This essay will first review existing literature and research on vocabulary. Then it will evaluate current ideas and strategies based on specific students and provide suitable teaching methods and materials. Finally, it will provide some recommendations.

2 Literature review

0.1 What is vocabulary?

The Oxford Dictionary defines vocabulary as a collection or list of words with concise explanations, definitions, or translations of the meanings of the words, either as separate word lists or as word books, now usually as part of an elementary grammar or reader [2]. Vocabulary can be defined as knowledge about words and their meanings. As well as can be divided into two forms, oral and printed [3].

To teachers, vocabulary also has different meanings. Sometimes it is used to mean to refer to visual vocabulary, which are words that students can quickly identify when printed. Sometimes it is used to refer to hard words that students encounter in content.

0.2 What is to know a word?

According to Nation's (2001) list we know that recognising a word involves form, meaning and use [4]. It requires learners to be able to not only recognise but also to spell, not only to listen to it but also to pronounce it. Along with knowledge of individual words, learners should also have knowledge of synonymy, antonymy, hyponymy, and the part-whole relation. Lexical knowledge includes knowledge of form (pronunciation, spelling, word derivations), position in grammatical constructions, collocations (co-occur words), functions (frequency and appropriateness), and association [5].

Proficient vocabulary learners have an understanding of the morphology and patterns of word meanings in English, including prefixes, root, and suffixes.

Knowing a word also involves the ability to use it in purposeful communication. It is not particularly useful to use vocabulary in isolation and out of context; it is only useful when the vocabulary is used in actual communication.

0.3 Vocabulary size and depth

With the continuous research on vocabulary, people have realised that vocabulary knowledge is multidimensional. Anderson and Freebody (1981) suggest that it is also possible to distinguish a person's vocabulary knowledge as size or breadth and depth or quality of vocabulary knowledge [6].

The size of vocabulary refers to the number of words the learner has known. Depth of knowledge refers to the degree to how well the learner understands and is familiar with the word [7].

In testing, the size of a learner's vocabulary is usually tested by naming objects in pictures or given nouns and verbs. For example, Nation's vocabulary level test requires candidates to match words to simple definitions [4]. Vocabulary size is generally measured through inferential test scores [8]. Nation (1990) also suggests that depth tests can examine how well participants know various types of vocabulary, such as spelling, pronunciation, grammatical, stylistic collocations and frequencies [9].

Breadth and depth are not opposites, but strongly related. The growth of both is affected by the frequency of inputs. According to the experiments conducted by Vermeer (2001), we can know that if a person knows more words, he can describe a word more deeply [8]. The size of vocabulary is usually assessed on the basis of the learner's ability to relate word forms to word meanings, but this alone does not ensure accurate comprehension. Therefore, learners must also develop depth of vocabulary.

0.4 Receptive and productive knowledge

A widely accepted convention is to divide vocabulary knowledge into receptive and productive vocabulary.

Receptive vocabulary knowledge is usually defined as words whose meanings can be recalled by the learner in listening and reading based on pronunciation or word forms. Productive vocabulary knowledge is usually defined as the ability of learners to spell words correctly, produce compositions and associations, and accurately use words in sentences to express their ideas [4]. Receptive vocabulary is the type of vocabulary that readers encounter during reading and listening. Productive vocabulary is the type of knowledge needed to use words in speaking and writing [10].

The assessment of receptive knowledge uses Vocabulary Level Test [9], and the assessment of productive knowledge uses Productive Vocabulary Levels Test [11].

According to Teichrow (1982), the learners' familiarity with words influences the switch of receptive and productive knowledge [12]. When the learners become more familiar with words, adding meaning to a word he knows, receptive knowledge gradually becomes productive knowledge.

It is widely agreed that a person’s receptive vocabulary is larger than his or her productive vocabulary [13]. Morgan and Oberdeck (1930) found that receptive knowledge grew faster than productive knowledge at lower levels [14]. And at higher levels, productive knowledge grows faster than receptive knowledge, but never to the same level as productive knowledge.

0.5 Vocabulary teaching approaches

The views about how vocabulary is learnt mainly relate to the strategies used by learners and the methods used by teachers to teach vocabulary.

Hunt and Beglar (2002) outline three approaches to vocabulary teaching and learning: incidental learning，explicit instructions, and independent strategy development [15]. Two approaches have been largely followed in vocabulary learning and teaching research to this day: the vocabulary can be learned incidentally, or taught explicitly and intentionally [16].

Intentional teaching means that teachers set clear goals for learners and use teaching strategies to achieve them. Teachers can help students acquire new vocabulary through direct instruction or presentation in the lesson. Intentional teaching is usually planned and managed and requires teachers to select specific learning activities and environments. The learning outcomes of learners are checked after vocabulary learning and prompt learners to learn and remember deliberately. Intentional teaching emphasizes student engagement and content understanding. Teachers take the role of leaders; they deliver information consciously and students receive it consciously. Research by psychologists has shown that intentional learning was shown to be superior to incidental learning (e.g., Eagle & Leiter, 1964; Thorndike, 1908) [17]. Intentional teaching requires teachers to have a wide understanding about how students typically develop and learn [18].

In applied linguistics, "incidental learning" means acquiring a word or expression without consciously committing the element to memory [19]. Incidental vocabulary acquisition is the learning of new words completely unconsciously and unintentionally after being exposed to them in a meaningful context [20]. Incidental learning is usually unpredictable. Incidental learning of vocabulary takes place through input, much vocabulary is acquired incidentally through general reading and general listening. Language is acquired subconsciously, which means when you acquire language, you are not aware that you are acquiring it. Your awareness is focused on the information, not the form [21].

In incidental learning, the purpose of learning is to understand the meaning of the text, not to study the relevant vocabulary. Incidental learning applies to both abstract and factual statement knowledge, and intentional teaching applies even more to factual knowledge [19].

Incidental acquisition of vocabulary through reading is a slow and error-prone process with minimal vocabulary growth [4]. Therefore, in order to increase the rate of incidental vocabulary acquisition, teachers should provide students with enough new words to repeat by giving them access to level-appropriate, clear, rich, and supportive written and spoken texts.

The research of intentional and incidental vocabulary acquisition has received attention from many researchers, but teachers and learners still have difficulty in determining the best way to learn vocabulary. In general, intentional learning is the purposeful learning of words and their meanings in a period of time. Incidental learning may occur over an extended period of time.

3 Discussion

The discussion is based on the Chinese primary school students' English level, learning situation and learning environment. Most Chinese primary students' English level is A1. Firstly, there will be a discussion about what words and knowledge should be taught to them. Then it will evaluate different strategies and methods and compare their advantages and disadvantages. In addition, vocabulary teaching materials will be complemented. Finally, suggestions will be given.

Some scholars such as Lenneberg (1967) believe that the best age to learn a second language is pre-adolescence [22]. Children with limited vocabulary before grade3 have reduced comprehension in the later years of primary school [23]. This shows the importance of teaching vocabulary in primary school.

Primary school students learn a foreign language probably because their parents send them to school, and they do not have the self-motivation and urgent need to learn English. We should design activities with fun and create a positive environment. Using incentives, setting goals, and other ways to turn external motivation into internal motivation.

0.1 What vocabulary and which aspects should be taught?

What vocabulary should be taught is mainly based on the needs of the learners and the importance of the vocabulary. Different words have different values for different learners.

In the lower grades, students are at a lower level. We can teach concrete words and then gradually become abstract. It should also consider the frequency and high frequency words should be the first vocabulary target for the learners.

Nation (2001) suggests these aspects, spoken form, written form, parts of words, concepts of words and the items they may be associated with, word associations, word grammar, the register of words, collocation of words and word frequency [4]. Learners must know what a word is pronounced and spelled [24]. Therefore, pronunciation and spelling should be the foremost elements to be acquired for primary school students. Some grammatical rules, such as the plural form, should also be acquired.

It is also important to know the meaning of words. The meaning of a word is mainly about what it means in the real world, namely its denotation [24]. Learning about synonyms and antonyms is also helpful for primary school students' reading skills.

Other aspects such as prefixes and suffixes. I think it is too difficult for primary school students and is not a priority for teachers to teach.

0.2 Strategies

I think that teaching should be carried out with intentional teaching as the main approach and incidental learning as complementary.

Firstly, intentional teaching has clear goals. Intentional teaching is focusing attention directly on aspects of words in order to learn them [25]. It helps students to acquire what they need to learn in certain time by systematically imparting knowledge. Because the time in the classroom is limited, teachers presenting knowledge to students visually can help learners refine their word knowledge. Students can also know the focus of learning and are conscious of knowing and remembering the vocabulary knowledge. This can develop self-control in students.

Secondly, intentional teaching can turn incomprehensible language input into comprehensible input. When primary school students learn L2, they have already basically acquired their mother tongue. Teachers can translate in the process of teaching and help them match the vocabulary of L2 with L1. During vocabulary learning, we are mainly focused on vocabulary association and matching. In order to enhance students' understanding of word meanings, teachers should provide students with rich conversations rather than learning in isolation.

As young learners have a weak capacity for intentional attention, their attention is easily dispersed, and it is difficult for them to focus on specific learning targets. Teachers should design teaching activities with fun and interesting, which can be done through games, videos and so on. During and after teaching, teachers can use fill-in-the-blank exercises and matching exercises to test whether they remember. Young learners have the characteristic of forgetting easily, and practice can help them to consolidate it over and over again.

Incidental learning can be used as an aid to help teachers teach vocabulary. Incidental learning can be gained through extensive listening, extensive reading, or other activities incidentally. In a study on Japanese EFL, it was found that learners showed significant growth in vocabulary knowledge when they encountered a word more times [26]. Due to the lack of reading skills of primary school students, it is difficult for them to understand the meaning of words through information from the context. This shows that teachers should choose reading texts that are at the students' level and vocabulary should appear frequently enough.

Neither intentional nor incidental learning can solve all aspects of vocabulary knowledge [27]. Scholars such as Nation (2001), Pigada and Schmitt (2006) argue that incidental learning is insufficient for L2 vocabulary learning, that intentional learning is more beneficial, and that the combination of these two approaches may be more successful in improving vocabulary [4] [28]. The research showed that the target words acquired from a combination of intentional teaching and reading were better than those from a reading-only group [29]. Teachers should combine these two strategies to teach word knowledge with intentional teaching and reinforce word knowledge with incidental learning, which can enable young learners to acquire more knowledge and skills in English.

0.3 Methods

The use of visual aids

In teaching vocabulary, teachers often use visual aids such as Using illustrations and Pictures. This is an attractive way to help learners understand the meaning of words more intuitively, to attract their attention to the material, and to stimulate interest in learning English. Several studies have shown that the use of visual aids can greatly improve retention of information and enhance students' understanding of unfamiliar knowledge [30].

3.3.1. Translation

Translation is a way for teachers to be able to quickly present the meaning of words in the classroom. L1 and L2 vocabulary are not stored independently. For second language learners, especially beginners, the use of their mother tongue can help them to make a direct connection between the target word and its counterpart in L1. But over-reliance on translation may result in learners not spending enough time and effort to understand the meaning of words.

3.3.2. Games

Games are activities with rules, goals, and an element of fun [31]. Games provide an enjoyable way for primary school learners to acquire vocabulary and increase their interest in learning English. Teachers can use games to increase learners' exposure to vocabulary by repeating words again and again. Games help students to deepen their memory of English vocabulary through repeated and unintentional use. The challenging and competitive character of the games motivates students to memorise and consolidate the vocabulary more diligently, thus improving the efficiency of memorization.

3.3.3. Situational presentation

It provides complete contexts and creates situations for teaching. When students know the specific situation, it is easier for them to remember the words and use them flexibly in actual communication. It can motivate students' interest in learning English and encourage them to be active. This method helps learners understand abstract vocabulary and consolidate the meaning of unfamiliar words. New words should not be presented in isolation or learnt through simple rote learning [32].

0.4 Materials

The use of other materials to complement textbooks can deepen understanding and provide more comprehensive learning. In order to adequately respond to students and their specific needs, teachers must be creative in their use of relevant complementary materials.

3.4.1. Word lists

Some scholars believe that word lists play an important role in learning the vocabulary of a language [33]. Using word lists to learn second language vocabulary is common. Teachers can design a variety of activities using word lists. Research has shown that vocabulary learnt through word lists is retained in learners' long-term memory [4].

Primary school teachers should use the frequency of vocabulary as one of the selection criteria when choosing word lists. Teachers can refer to several strategies suggested by Thornbury (2002) when using vocabulary lists. It can also be done by the teacher randomly reading words from a word list and the learners match the pronunciation and writing form by ticking the words they hear [4].

3.4.2. Graded readers

Graded readers are books written or modified specifically for second language learners using controlled vocabulary [34]. Young learners are not at the level for reading real texts and graded readers are considered to be an ideal source for vocabulary learning. It provides a range of books of increasing difficulty that teachers should select according to the level of the learners. Because of the high frequency of word repetition in them, teachers can use them to promote incidental learning.

4 Conclusion

It is necessary to have a large vocabulary to acquire a second language. This essay presented that teachers should choose the vocabulary and aspects to be taught based on learners' needs. Secondly, teachers should identify strategies for teaching vocabulary and provide students with different methods of learning. Finally, teachers should have a choice and complement the teaching materials. However, because of space limitations, there are many parts that affect primary school vocabulary teaching and learning that have not been explored.