This study examines written errors in a corpus of 30 compositions produced by 15 students of English as a second language (L2), whose first language (L1) is Spanish. Their ages range from 10 to 11. This paper identifies grammar errors as the most frequent due to L1’s interference in L2 learning. Positive, focused, indirect written feedback is proven to be the most effective, and the L1 seems to help the students to understand the teacher’s metalinguistic explanation to correct errors and avoid mistakes. These results provide insight into language learning given that they offer information regarding the teaching practice.