This electronic learning game covers addition, subtraction, times tables and maths multiplication and division. It is a bit bigger than a DS lite and it is easy to hold.

There are 8 levels of difficulty. Levels 1 & 2 allow you to do drills by choosing a number to practice. You get 10 questions for each drill.
At level 1 you get a sequential order so if you are drilling 5 in addition it goes 5+ 1, then 5+2, 5+3 etc.
At level 2 the questions are random order so 5+1 then 5+8 and so on. As you get better you try to beat your previous time. This makes it a good toy for self directed learning and practice.
At level 3 you still have basic maths facts (+, -, x, ÷) 0 to 9 in non-sequential order and drill numbers are randomly mixed.
At level 4 you have 2-digit numbers with 1 digit operators without regrouping.
At level 5 you add 2-digit numbers to 2-digit numbers, subtract 2 digit numbers from both 2 and 3-digit numbers, multiply 1- or 2-digit numbers by a number ending in zero, divide 3-digit numbers by 1 digit numbers.

And so on until level 8. Maths Whizz by Learning Resources.