[Kiteboarding] Handling the kite can be largely taught on shore, as kite boarding evolved from beach kiting. On the water, recovery from falling is relatively easy (the kites, especially the newest models, stay normally aloft to pull the rider out of the water, with little effort) as is changing tacks, even in strong wind. [Windsurfing] Handling of the airfoil (sail) is learned mostly on the water with some dry practice for beginners. Advanced high wind techniques (e.g. water start) can only be learned in deep water. Recovery from falling is easy with a little practice, as the rider needs to either up haul the sail standing on the board or water start, which both take some strength and balance. Water starting is an advanced technique that just takes some teachable techniques and practice. At the same time, the risk of falling is always there (experts can go days without a fall but a missed jibe might happen). Tacking becomes more difficult in stronger winds, so most riders switch to easy jibes. [0] 
Learning Curve