This puzzle won the Shannon O'Hannanan Public School's Puzzle Club contest. As the prize, we are letting the winner type out his puzzle on the Puzzling Stack Exchange for all of you to solve. Our winner is Simon Swive (Grade 6).
The answer to the puzzle is a noun:
11 22 33 44
55 66 77 88
99 1010 1111 1212
1313 1414 1515 1616
1717 1818 1919 2020
212121 2222 XY
It should be noted that how the groups of numbers are arranged is irrelevant, so long as the spaces are maintained (they can technically be grouped in any way). The grouping chosen was designed to help you solve the puzzle.
It has several accepted synonyms. You can say it in a sentence, like:
"My son is a _________".
or
"Does your little girl have ________?"