I started studying Spanish in 7th grade and all the way through middle school and high school my teachers taught me Spanish by using English. Only when I got to university did my teachers start using Spanish to teach Spanish.Nowadays, people frown upon using students' L1 in class. While this might be because many of the teachers teaching EFL don't speak the students' native language. The other reason might be because teachers feel that students can learn faster if they just use English in class.
While this may be true, imagine how you would feel if you walked into a classroom and the teacher only spoke the target language. As a complete beginner this might be extremely daunting. You might feel frustrated or even give up. Granted, there are some gifted teachers who can only use the target language and have students understand, but many teachers don't adjust their language enough and both the students and teachers end up feeling frustrated.
I know from personal experience, when I started to study Korean, the teacher only spoke Korean. It wasn't the simple L+1 either, it was more like L+10. I ended up feeling very frustrated and upset at the teacher as well as myself. If she wrote on the board, I'd have to look up practically every word. She moved very quickly through the lessons as well. Even though I didn't understand, I didn't have the language ability to ask her. Nor did she have the English needed.
So what should you do? First, you need to adjust your language. Speak slower and simplify your vocabulary. IF you speak the students' L1, you might want to use it every once in a while. I'm not advocating saying everything in the students' L1 and then translating into English, but a word or two here and there can help. If you don't feel comfortable speaking the students' L1 or don't know it, try writing on the board or asking a higher student to help translate. If you're dealing with very low students, you might want to write what you're going to say on the board first, so that students can read along. This allows them to listen and read what is being said.
