The correct usage of CAN and COULD in American Casual, Spoken English using "Modal Verbs", general rules to go by (never hard and fast or forever, always, aka: always exceptions but here's a really good start)
you can practice toefl reading and check the time that you spend in each question
Idioms: 5 Common and Simple English Idioms Poster. It think this would be a great poster to have displayed in the classroom while working with idioms. The students could even make their own version of this poster to display at the end of our unit.