Иванов, к доске! = Ivanov, please come to the blackboard! (to report on homework, solve a problem, give a presentation, etc.)
Можно выйти в туалет? = Can I go to the toilet?
Можно выйти? = Can I leave for a moment? (literally: Can I go out? A shortened version of the above phrase.)
Через сколько минут звонок? = How long till the break?
Какой сейчас урок? = What class is it going to be?
Что задавали? = What was the homework assignment?
Откройте учебник на странице 154. = Open page 154 of the textbook. (addressing a group)
Запомните... = Remember... (addressing a group)
Дай списать! = Let me see your answers! (considered to be cheating)
К доске пойдёт... = The pupil who will go to the blackboard is... (used by a teacher while picking a name from the class roster)