My 3.5 year old is bilingual, with English spoken at school, not at home. How do I evaluate his language skills to see whether he can do well on the OLSAT® in English? What I can I do to enhance his skills? Is there research on whether being bilingual presents a disadvantage for children being tested?

Let’s start with the easy question first—the role of bilingualism in language development. There is research on the question you have posed. It indicates that if a child has language problems (such as articulation problems, auditory discrimination difficulties, etc.), then bilingualism is an added burden. However, if there are no such problems, bilingualism is actually an advantage, ultimately leading a child to have increased language abilities along with having the advantage of being skilled in two languages

Now for the more difficult questions that you have raised. Those questions represent two important,  but different issues. One is aimed at determining your child’s skills in English; the other at what you can do to enhance those skills.

In terms of the assessment issue, if your son is not accustomed to you speaking English with him, you may not be the best one to evaluate his English language skills—since he may be “thrown” by the change when you suddenly switch to English.  However, if you have a friend or relative who is familiar with language development (for example, a teacher of preschoolers), then a play session between your child and that person can be quite revealing and provide you with the information you are seeking.

In terms of the enhancement issue, an excellent activity can be found in reading appealing books to your child on a steady basis. This would mean that you would have to make conversations in English a regular component of your interaction with your child. If you cannot do that, then you may need to hire someone who can carry this out. The story telling should be relaxed and not an endless test of what your son is “taking in.” The stories present a rich language base that captures a child’s interest and they enable a child to build increasingly complex language abilities. In addition, if the story telling atmosphere is a relaxed one, young children become eager participants in the exchange—questioning what is happening, offering alternatives to what did happen, sympathizing with the characters and so on. So along with hearing good language, the activity leads to increasingly sophisticated conversational abilities.