By Tami Luhby

The job market might be getting better ... but not for teens.

Their unemployment rate remains above 20 percent for the 40th month in a row, the first time this has happened since the government started keeping records in 1948.

Last month, it edged up to 23.8 percent, roughly the same as a year ago and up a bit since December. The national unemployment rate, meanwhile, has fallen to 8.3 percent.

Some 31 states and the District of Columbia have teen unemployment rates above 20 percent. Washington D.C. ranks the worst with an unemployment rate of 48 percent, while California places second at 35.2 percent.

This is not good news for teens' summer employment prospects. The last few summers have not been kind to young workers.

States' interest in raising minimum wage could make it even tougher for youngsters to find work because it could force employers to cut back on hiring, according to the Employment Policies Institute, a right-leaning research group that has long advocated against minimum wage hikes.

Eight states raised their minimum wage at the start of the year, and another 15 are considering doing so, according to the institute.