Habitual tense is for ideas that happen regularly, i.e. there's a pattern. For example, brushing ones teeth. You wouldnt say "every morning, I am brushing my teeth", you'd say "every morning, i brush my teeth". In this case, student preparing farms that belong to their schools are activities that happen regularly, spent some time in TZ and seeing students go to school with gardening tools is quite common, at least in the rural areas
I asked the question because in this specific sentence I have trouble figuring out the precise situation in which the Swahili sentence would be used. "Students prepare a farm" is obviously a grammatical sentence, but the articles seem uncommon. I can imagine it being used, but in only such narrow environments that I would be surprised if the Swahili sentence has the same strictures.