摘要:Abstract The present paper investigated a number of grammatical errors committed by young learners around the age of six to thirteen and adults between the ages of eighteen and twenty-five. They were at the same proficiency level (elementary level). Adults were studying the “Intro” book from the Interchange series and young learners, “family and friends 2”. The grammatical points were taught deductively so that they could become more familiar with them and their errors could be removed. The classes were held three sessions per week, lasting six weeks. At first, Pre-test was administered and 40 students out of 60, whose scores were somewhat identical, were chosen. Their errors were categorized into morpho-syntactic and lexico-semantic ones. Towards the end of the course, a Post-test was administered. The errors were classified into the same two groups. Afterwards, the errors were analysed. The grammatical errors made by these two age groups could not be remedied during the whole term in the classroom. Errors of 20 young learners and 20 adults in four classes (each class consisting of 10 students) in the academic year of 2012 were examined. Findings showed that most of adults’ errors were inter language errors, indicating the influence of the mother language, while most of young learners’ errors were due to overgeneralization.