My Abby (whom I think might be ADHD and possibly ODD)... has a hard time with threes.
One, she skips 13 everytime she counts. Even though I hit the teens hard and have tried to improve her counting, 9 weeks later, she is still counting about the same as she did when we started. This is if she is rote counting, counting items, adding one more, anything....
Not a big deal... lots of 5 yr olds skip numbers here and there.
However, she really struggles again when she gets to the thirties. I'm starting to see a pattern. She says "firthy free" instead of "thirty three"... then it blends and mixes up with the forties... She says 13 wrong, too.....
She confuses 13 and 30... a lot... she blends 13 with fourteeen.
We have used objects, used number lines, measured items, hundreds charts, hundreds chart activities, etc... I've tried to use money, time, etc... It's like it's only sorta making sense, and when it does one minute, the very next moment she has forgotten.
That being said, I wondered if she is struggling with them so much because she is saying the (three) words wrong. She's not maybe identifying between the two. So, I started trying to get her to put her tongue on her teeth for the "th" sound... Only now she's so concerned about saying it that she is even more confused about the counting.