Personally Ursinus and Olevianus are great (obviously) but they don't work well for your average bible study.

I have heard good things about G.I. Williamson's book but I have never used it myself. I wrote my own lessons on the Heidelberg and have also used Visscher's "I Belong" for high school students:

I Belong

__________________
Rev. Daniel Kok
Pastor of Grace Reformed Church (URCNA)
Leduc, Alberta CANADA
Church Blog

"there is no creature, either in heaven or on earth, who loves us more than Jesus Christ"
Belgic Confession, Article 26

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