At our Tutors Roundtable on June 13, 2007, we shared many wonderful ideas and resources to help our learners improve their English language skills. Here is a list of some of the titles mentioned at the roundtable:
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Grammar Wise 2
Focus on Grammar
What a Life!
Idioms for Everday Use
The Only Grammar Book You’ll Ever Need
American Heritage Dictionary of Phrasal Verbs
Do you have any other suggestions?