i want to teach my boy arithmetic. my current 'best' idea, is to have a board with a few columns with nine spaces in each column. headings from right to left would be (units,tens, hundreds etc.). nine small plastic discs showing value of +1 unit. nine discs showing value +10 units. nine discs showing value +100 units, et al, would allow numbers to 999 a 'bank' with spare discs showing the above values, plus spare discs showing the above values but in a negative form, (to be used for subtraction by 'cancelling'.) the idea is, that a number such as six hundred and fifty four could be physically shown by four discs in the bottom four spaces in the units column of the board, each llabelled (+ 1 unit). five, (+ 10 unit) discs similarly placed in the tens column of the board. six (+ 100 units) in the hundreds column. addition and subtraction could be performed adding discs from the 'bank' into the columns. i feel that physical manipulation of numbers would lead naturally to the concept or mental manipulation. do you think this is a good method of teaching arithmetic and can you suggest any improvements.