First learn the doubles. Students can easily learn doubles by chanting to the "Sound Off" military cadence like this: "One plus one equals two." (echo). "Two plus two equals four." (echo). "Three plus three equals six." (echo). Chant up to "12 plus 12 equals 24". (echo). After learning the doubles, start teaching the doubles plus one math trick. If 5+5 equals 10, then 5+6=5+5+1 which is 11. Or how about 7+8=7+7+1 which is 15! After the doubles plus one math trick is easy for the kids to do, they can learn doubles plus two! 6+8=6+6+2 6 plus 6 equals 12 plus 2 more is 14!
Kids can easily learn the math facts that make 10 like 6+4=10, 7+3=10, 8+2=10, 9+1=10. 0+10=10 when they see the whole group of facts together. They also need to understand that 7+3 is the same as 3+7. Kids can use the Make Ten math trick when adding numbers with more than one digit. For example 27+43, kids look for Make Ten facts like the 7+ 3 in the ones column. Then they place 0 in the ones column and add one group of ten to the total of the tens column. Think 10+20+40=70.
Adding nine to any number is easy if you remember the math trick nine "jacks" (steals) one from other numbers. For example in the problem 9 + 8 remember 9 jacks 1 from 8 to become 10, so then you have 10+7=17. Note that the word "borrows" just doesn't resonant like the idea of "jacks." Additional examples: 27+9=26+10=36; 458+19=457+20=477