A very simple starting point would be the following from a paper by Jordan, Kaplan, Ramineni & Locuniak Development of number combination skill in the early school years: When do fingers help?:
Finger use for math calculation is natural and intuitive. Fingers are readily available and well suited to our base-10 number system. However, many teachers and parents question the value and appropriateness of ﬁnger use in elementary school, even though most contemporary math curricula encourage concrete representation and manipulation of quantities. ...Our ﬁndings suggest that in kindergarten children should be encouraged, or even explicitly taught, to use their ﬁngers.And so, if we want to re-energize American education we need to develop specific strategies to systematically re-engage our children's hands in learning. An effective part of that strategy is Wood shop!