Interference is the process whereby someone makes mistakes in automated tasks because the task asks for something different than what he expects. Interference is often the basis of slips of the tongue, such as mixing up the names of family members. A well-known way to test interference is the so-called Stroop task. Someone is asked to read the color of a word. That is not a problem as long as the word “red” is also printed in red. But things get difficult when the word “red” is printed in green. The brain areas that are important for this task develop well into adolescence. The older an adolescent is, the better he is able to suppress irrelevant information, such as the color in which a word is printed. For the education of adolescents it is important to know that they are not able to filter out irrelevant information. So learning French words with the radio on does not make learning those words any easier. It also follows that multitasking is even more difficult for adolescents than it is for adults. Their brains are not yet able to perform different tasks at the same time. Research among adults shows that they too are hardly capable of multitasking.