@inbook {LadKor-DTBLEPVUAAT-2013,
	title = {Designing a technology based learning environment for place value using artifact-centric activity theory},
	booktitle = {Proceedings of the 37th conference of the International Group for the Psychology of Mathematics Education. Mathematics learning across the life span},
	volume = {1},
	year = {2013},
	pages = {188-192},
	keywords = {refereed},
	author = {Silke Ladel and Ulrich Kortenkamp},
	editor = {Anke M. Lindmeier and Aiso Heinze}
}
