We have a prep sink & use it all the time!

The "secret recipe" for a useful prep sink includes:

• Location, location, location! It should be where you like to prep the most and where it's easily accessed from the Cooking Zone. Ideally, across from the cooktop/range or next to the cooktop/range along the perimeter.
• Size! It should be a minimum of a sink that fits in an 18" sink base and takes up the entire sink base. Any sink that will fit in a sink base < 18" is probably a bar sink, not a prep sink. Bar sinks are small and intended for dumping or filling a glass of water.
• Workspace! There should be sufficient workspace on at least one side of the sink -- at least 36", but 42" or more is better. (If the sink & range/cooktop are on the perimeter, the workspace should be b/w the sink and range/cooktop.)
• Workflow! Is it located where it's needed? (see Location above).

• Bottom line: If the prep sink is located properly and sized properly, it will get used. It's not about Kitchen size, it's about the layout of your Kitchen and how it functions with the prep sink. Some Kitchens do not have a great layout without a prep sink and others don't need one b/c the layout is already very good. Unfortunately, most production builders don't proved a good Kitchen layout in their houses.

Regarding homework use of the island & water. If your island is properly sized, it won't be an issue. If you have seating in the island, it should be at least 42" deep with a seating overhang of 15" (minimum recommended for counter-height seating). That's plenty of space b/w the sink and someone working on the island. Plus, as others have stated above, the homework years will be very few and be over before you know it. While young children might do their homework at the island, teens will not want to -- they'll want to do it in their bedroom or other more-private spot (at least that was my experience and that of my family & friends).