Ladel, S., & Kortenkamp U.  (Submitted).  Number concepts ?- processes of internalization and externalization by the use of multi-touch technology Silke Ladel and Ulrich Kortenkamp.  Early Mathematics Learning.  

[Gast]  (2014).  Early Mathematics Learning.  (Kortenkamp, U., Brandt B., Benz C., Krummheuer G., Ladel S., & Vogel R., Ed.). 

Ladel, S., & Kortenkamp U.  (2013).  Designing a technology based learning environment for place value using artifact-centric activity theory.  (Lindmeier, A. M., & Heinze A., Ed.).Proceedings of the 37th conference of the International Group for the Psychology of Mathematics Education. Mathematics learning across the life span. 1, 188-192.