The meaning of a suffix

I asked Jonathan what does the suffix -ly mean. He didn't know.

I had him and Chris think of words that end in -ly. (gently, beautifully, carefully)

I asked Chris to use gently in a sentence (I gently patted the cat) and Jonathan to use gentle in a sentence (My back felt gentle).

I said, "Gently shows us HOW he did something and 'gentle' tells us what your back IS."

I wrote down "gently- doing" and "gentle - is."

Then they made sentences with the other words, and I begin to write those words, also, with "doing" or "is" beside them.

Jonathan's eyes lit up. He knew then what -ly does to a word. "-ly means how someone is doing something."