Have a look at the different geoboards below. You might also find the Square Dotty Grid and Isometric Dotty Grid environments useful.
Square
To change the size of the board use the slider.
Click on the draw line tool and then click on two dots to add a line between them.
Circle
To change the size of the board use the slider. You can choose whether your geoboard has a centre peg.
Click on the draw line tool and then click on two dots to add a line between them.
Rectangle
To change the size of the board use the sliders.
Click on the draw line tool and then click on two dots to add a line between them.
If you would like to work on paper, the Printable Resources page has links to printable sheets of circles with a range of numbers of circumferential dots.