Should I buy a youth board my child can grow into?

No. This is the most common and harmful mistake in youth snowboard purchasing. A board that is too long or too stiff will be difficult to turn, hard to control, and more likely to cause edge catches. It will slow or stall your child's progression and reduce their enjoyment. Buy the board that fits now, not the one that will fit next year. The cost of replacing a board when it is outgrown is far less than the cost of a child who quits the sport because their equipment fights them.