This study investigates the impact of socio-economic factors on the English vocabulary size of primary school pupils in Malaysian new villages. It integrated both quantitative and qualitative methods through surveys with demographic questions and adapted Controlled Vocabulary Levels test together with interviews involving pupils and their parents. Most pupils demonstrated difficulty in reaching vocabulary mastery at the 2,000-word basic level which serves as a minimum requirement for functional language capabilities. Vocabulary learning advancement at less common word levels showed strong associations with fathers' occupations and household income even though parental educational background demonstrated minimal effects. The qualitative data showed strong evidence for how parental involvement through learning facilities provision and direct instruction along with educational participation enhanced vocabulary acquisition for pupils. This study demonstrates that socio-economic differences must be addressed to boost English language learning in marginalised pupil populations because it reveals approaches to reduce these inequalities.