We recommend speaking with the teacher and understanding from her which difficulties she's noticed and why she thinks he needs an assessment. Additionally, you should pay attention for a number of signs that are likely to suggest the presence of learning disabilities: does the child have difficulty learning the colors, numbers, shapes, the Aleph-Bet? Is there a problem with understanding and following directions? Does the child have difficulty with or avoid activities such as drawing, coloring, cutting, and/or building puzzles? Does the child have trouble sitting through rikuz (morning meeting time)? How does the child get along with friends and adults who surround him? Does the child have difficulty obeying the rules of games or group activities? And more.
In a case where there are significant difficulties in a portion of these areas, then it's probably a good idea to go for an assessment in which the nature and source of these difficulties will be clarified. Afterwards, it will be possible to treat and to ease the child's entrance into 1st grade and the beginning of school.