Word Tiers

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Tiers of Vocabulary

In their three-tiered model of vocabulary development, Beck, McKeown, and Kucan (2013) classify words in tiers.

Tier 1: common, everyday words that most children enter school knowing already.
- E.g. apple, bird, mouse, shoe.
Tier 2: high-frequency words that are used across the different subject areas and are important for students to know and understand.
- E.g. evaluate, yield, limiting.
Tier 3: subject-specific vocabulary. The words that are often defined in textbooks or glossaries.
- E.g. electromagnetism, endothermic, chloroplast.

Cell structure and function are usually taught in two to three lessons in Year 7 science. Consider the key terms used:
- cell, cell surface membrane, cell wall (cellulose), chlorophyll, chloroplast, cytoplasm, mitochondria (respiration), nucleus and vacuole.
Students have to recognise the structures listed, be able to name them and understand the functions of the structures within a cell.

This vocabulary is known as tier 3 vocabulary, low-frequency domain-specific words.
The number of keywords related to science is vast, for example in a published resource for the GCSE topic of photosynthesis there are 68 science-specific keywords.

Consider the word tissue. In biology, it defines a group of similar cells working together for a specific function. In this case, it is an example of tier 3 vocabulary, a domain-specific word.
However, the vast majority of Year 7 students will be familiar with the everyday meaning of tissue: a thin piece of a paper-like material that you blow your nose on. In this case, it is a tier 1 word.
This is an example of how confusion in science can arise due to the scientific meaning of words being different from their everyday meaning.

If a student does not have secure knowledge and understanding of tier 2 vocabulary, reading scientific text or assessment materials can be challenging. To read text effectively it is said that students must know 95% of the vocabulary in the text.
Tier 2 words can be problematic for students if there is not a clear understanding of the word.

Examples of words in a GCSE chemistry 2018 exam paper:
- Tier 2: give, define, describe, determine, estimate, suggest, calculate, evaluate, explain, balanced, refuel, compared, experimental, trends, associated, limiting, yield, batch.
- Tier 3: acids, ions, formula, compounds, protons, neutrons, electrons, atom, transition metal, electrode, alkaline, isotopes, endothermic, electrolysis, gas, oxidation.

Communicating effectively in science requires vast knowledge and understanding of science-specific keywords.

Wellington & Osborne (2001) classify science-specific vocabulary using the following classification:
- Level 1: naming words e.g. vertebrae, conical flask, oxygen.
- Level 2: process words e.g. combustion, evolution, osmosis.
- Level 3: concept words e.g. work, energy, pressure.
- Level 4: mathematical words and symbols.

However, ensuring students can understand the vocabulary does not fully allow students to embed scientific concepts.
For students to ‘learn’ the science, they have to think deeply about how the key terms are conceptually linked.
For example:
- oxygen is linked to photosynthesis because it is a waste product of the latter.
- glucose is linked to respiration because it is broken down into CO₂ and H₂O.

Strategies to teach unfamiliar scientific vocabulary:
- Say the word to students using their correct pronunciation.
- Write it on the board – it is vital to write it out clearly and ask students to write the word larger than usual and leave plenty of space around it.
- Break the word down into its parts – you can use different colours of pens for this.
- Repeat the word one more time emphasising the different parts of the word.

Strategies to teach unfamiliar scientific vocabulary:
- Discuss the etymology of the word. It is useful if you can link the word to everyday language that the students are familiar with.
- State an example sentence using the word and get students to write their own sentences using the new words learned.
- Regularly reinforce the new vocabulary by revisiting using a variety of word games, bingo, hot seat, dominoes and spelling tests.