On a purely technical level, if the writing in pencil is too light, switch to a softer lead. The marks will be blacker without any extra pressure being required. The standard writing pencil is an HB (right in the middle). A 2B will give a nice dark mark without a lot of pressure or a lot of extra messiness.

Have you tried any sort of ergonomic grip? I think some of my issues were from gripping too hard and we tried using grips that relieved some of the pressure and made the process less painful.