Learning another language which is crucial for academic and professional purposes has been an important focus of research. While learning second language, certain forces related to the language affect this process. One of those forces is the interest of this study. Thus, current study investigates how the mother tongue affects students writing abilities, who are taking English as a compulsory subject in middle school whose native languages are Urdu and Punjabi. Without language, education process in classroom would not be possible. Students experience difficulties in native language when speaking and writing English due to interference. Current research focuses on influence of mother tongue on Pakistani pupils' development of writing skills while studying English as compulsory subject in the classroom. A random sample of 50 pupils in grades 6, 7, & 8 aged amid 11-14 years was chosen from 3 schools, all speaking Urdu & Punjabi as their mother tongues. The Contrastive Analysis Model developed by Robert Lado (1957), proposed by Ellis (1985) was used to analyse data. Results reveal that errors in word order, grammar, & spelling were caused by L1's interference in pupils' writing in target language. Findings suggest that teachers should do the need analysis of the students at beginning of sessions with help of relevant and appropriate tools.