As far as I know it's never recommended to use the mother tongue in class while teaching a second language. On the other hand, according to what the experts say, (e.g. Jeremy Harmer) it's not possible to ignore and put aside the mother tongue completely. But you must do your best to bring it to zero.
I've been to this situation myself. When my students have difficulty understanding something, I often kill myself to make them understand the matter in English (by gesticulating, miming, using realia, giving examples, etc.). If most of them understand, I've been successful. If most of them don't understand, I'll take the last remaining weapon which is "the mother tongue".
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