There is no need to replace a chalkboard that just needs a little help. Depending on the problem your chalkboard is facing, there are several options, so read on and bring that old chalkboard back to life.
Prime your board with more chalk. This sounds counter-intuitive, but often your chalkboard problems can be solved with this method. Wash the board with a wet sponge and allow to dry completely. Rub a stick of white chalk (using the side) all over the board, then erase. This could solve your problem by adding a little chalky grit to the board for the writing to adhere too.
Switch brands of chalk. Many cheap brands of chalk are poorly made and are too oily. Try switching to a higher grade of chalk and your chalkboard may work better.
Try a chalk ink marker. This is a marker that looks like chalk but applies with a marker. Works on chalkboards, glass, plastic and metal. Wipes off with water. It's cleaner and easier to use than traditional chalk (see Resources below).
Refinish your board. If you've tried everything else, it may be time to refinish your chalkboard. Chalkboard paint can be purchased as a can of paint or as a spray paint. It is found at home improvement stores and the paint departments of most discount stores. You will need painter's tape to mask off the chalkboard's frame. Chalkboard paint applies like any other paint (see Resources below).