For some interactive tests try maths online by Franz Embacher and Petra Oberhuemer. Some are multiple choice, there are also other types of tests including matching exercises.
These could make good lesson starters.
Most of the resources are for older students though one or two on algebra might be useful for younger students.
If you are looking for further interactive tests like this see extensive collections from Dynamic Maths Worksheets; see also InterActMath which is designed to accompany Addison-Wesley and Prentice Hall textbooks but does stand alone. Choose a book and a chapter for several exercises, the view can be enlarged so could be displayed on an interactive whiteboard. The questions are multiple choice. It is possible to view examples with complete explanations. A keypad is provided for entering mathematical expressions.