I want check this sentence for writing in a recommendation letter that a teacher wrote :
"he took three undergraduate courses with me which for all of them he was a well above average student"
please help me.
Be careful with your spelling. Both words in your title were spelt incorrectly. It should read "checking grammar". In fact, the title should have been completely different. The forum guidelines ask that your thread title contain some or all of the words you are querying. A good title would have been "He took three undergraduate courses ..."
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.