According to wikipedia:
Cancellation (supplemental)- children scan random and structured arrangements of pictures and marks specific target pictures within a limited amount of time.
This page -
http://testingforkindergarten.com/u...rb-how-is-it-different-from-the-old-test has much more info:
With this subtest, a sample of which is shown from the test publisher’s brochure, children ages 4:0 to 7:7 are shown a series of related objects – in this case, items of clothing. They are then shown an organized (i.e. in rows) and later, an unorganized (i.e. “random”) page filled with items of clothing mixed with other child-friendly items like toys, animals, cars, etc. The child must use his ink dauber and stamp each item of clothing that he sees within a specified time. Some good activities to do with your child to build the skills required to do well on this visual-recognition/classification subtest are the “Spot it, Jr.” games, which can be found at Amazon.com. I would also recommend “Where’s Waldo” books, also available at Amazon.com. Another great item to build your child’s visual-spatial reasoning skills needed to perform this activity are the “I Spy” books. You can buy these at the pre-school level and let your child work her way up to trickier and more complex arrays of hidden items. Children love these books and they have no idea that they are building their non-verbal intelligence when they work with them. You can also get these books at Amazon.com.
Looks like he might have not understood the directions, or not been interested, if he did well on all the other subtests. I would imagine this subtest could be highly affected by vision challenges or fine motor control issues.