The aim of this study was to identify effective teaching strategies for vocabulary acquisition for primary school-age children in natural sciences. Primarily, using qualitative method observation, it was empirically shown that the primary vocabulary instructions used during natural science studies were indirect incidental word learning activities such as conversation in the classroom. A test was standardized from Homegaard and Johansson Kokkinakis (2006) to asses and measure pupils’ breadth and depth of vocabulary knowledge for vocabulary words that were used during science class. The conducted test showed that the pupils’ trough incidental word learning had low vocabulary acquisition, primarily because of the everyday language used in a scientific context, leading this study to aim to answer the following questions:  

Will providing explicit instructions for word acquisition increase pupils’ vocabulary?  

Which possible explanations are there for the vocabulary increase?  

An intervention practice was conducted to improve vocabulary acquisition, using five evidence-based suggestions for meaningful vocabulary intervention activities, provided by Steele and Mills (2011) and Becks, McKeown and Kucan (2002). The steps are based on explicit instructional activities which were used in teaching natural science. The same test that was used to asses and measure pupils’ breadth and depth of vocabulary knowledge of vocabulary words was used after the intervention. The empirical results showed that instructional strategies providing explicit instruction were successful in increasing pupils’ breadth and depth of vocabulary knowledge. Hence, this study identifies the empirical link between vocabulary instructions and vocabulary acquisition, as to increase the pupils’ breadth and depth of vocabulary knowledge, by the acknowledgement of the difference between everyday language and scientific vocabulary with explicit teaching of the scientific language.