TABLE A1.

Trained conceptual level, skills and games/tasks applied in the training.

Conceptual level	Skill	Game/Task	Order of occurrence in the training. Games were applied with increasing difficulty.	Occurred N-times in training
Finger gnosis (not related to number)	Motoric accuracy	“Finger tapping” with each hands separately and together	1	5
	Motoric divergence	“Labyrinth”: tracing a way through a labyrinth with all fingers, separately	2	4
1-to-1 mappings of finger and number	Verbal finger-number mapping	“Naming the fingers,” i.e., thumb, index finger, middle finger, ring finger and pinkie and mapping the right numbers (right hand - 1-5 and left hand 6-10)	3	4
	Visual finger-number mapping in association with learning visual Arabic digits	“Tracing numbers” 1-10 on a sheet with the respective finger of the right (1-thumb, 2 - index finger, 3 - middle finger, 4 - ring finger, 5 - pinkie) or left (6-thumb, 7 - index finger, 8 - middle finger, 9 - ring finger, 10 - pinkie) hand	4	3
Ordinal finger-number associations	Counting	“Finger counting” forwards and backwards and starting with different numbers	5	3
		“Counting objects.” Children should show the counted objects with their fingers.	12	4
		“Clapping”: counting the clapping of the trainer and other children. Children should show the number of claps with their fingers.	13	5
	Ordering (Ordinality based on cardinality)	“Train-Game” with groups of 3-5 children. Each child got an Arabic number. Children had to show their digit with their fingers and order themselves in the correct numerical sequence like train carriages without talking. The number sequences were either continuous with missing “carriages” in between, e.g., 3, 5, and 9	14	6
		“Order card desks” with fingers, digits and points into the right sequence (from 1 to 10)	15	3
Cardinal finger-number associations	Verbal and visual finger to number and number to finger mapping of the respective cardinalities	“Corresponding number” naming the corresponding number to shown fingers (6) The trainer showed a finger-number pattern for a few seconds while saying a rhyme. Children had to recognize the finger-number pattern and show it with their own fingers and say the corresponding number. (7) Later, single children were allowed to show a pattern and appoint another child in solving the task.	6 and 7	12
		“Story-time” detect numbers that were hidden in stories and show the cardinality of the numbers with their fingers”	8	9
		“Memory” with cards displaying fingers and numbers	9	4
		“Bingo” with finger cards Children had to mark numbers on a sheet	10	7
		“Domino” with combined finger and number cards	11	6
Number relations: Base-10 and place-value system	Completion to 5/10	“Completion-Game” showing how many fingers are needed to 5 and 10	16	3
		“Completion” (to 5 and to 10) with cards displaying fingers	17	4
	Double numbers	“Double numbers” children should show the double number (with the fingers) to fingers shown by the trainer	18	3