well you should probably be swinging a -8.5 (31 length and 22.5 weight).

How tall is he/she and how much do they weigh? What may be a good size for one could be too heavy/light for another.

I always look at what they were using before, consider what they liked and disliked about the old bat. Also why do they need a new bat?

Do they like wood or metal? How much do you want to spend? Does color make a difference?

depends on the kid, hieght/weight, strength, skill level, etc. too many variables to say (blank) is the best. I'd use the chart that the manufactures show, then take into consideration some of the factors that I listed.

If your not sure, always go lighter. (and the color, color makes a big difference :)