My ex husband and I live in Wisconsin. He is angry with me over the cost of an educational club I put our son in. Is he obligated to pay half?

One would need to review your divorce papers/settlement agreement to answer your question. If you have shared or equal placement and are using the shared placement formula for payment of child support, usually, variable costs are split in some pro rata fashion. An educational club may be considered such an expense. Also, if you have joint custody, you need to discuss this in advance with your ex and if they don't agree, they may not be obligated to pay.