An easy way to teach children the difference between rhythm and the steady beat is to use heart beats like in my worksheet Rhythm Heart Beats. When I taught music in school, I had a flannel board with nice, big, red hearts. But in piano lessons we can do activities on paper and guide the student one-on-one.
This is one way to explain 8th notes and teach rhythmic dictation at the same time. Explain to your student that the beat in music is like a heart beat. Depending on the age, you can use the metronome while the student taps their chest. It’s fun to speed it up and slow it down. Later you can give them this worksheet and let them tap the hearts with their finger or pencil eraser while you chant “rain, rain, go away”. Be creative! If your student has trouble, you probably need to do more activities keeping a steady beat before you go on.
When the student is ready you can explain that a quarter note is one sound on the (heart) beat, but an eighth note has two sounds on the beat. Repeat the “quarter, quarter, 2 8ths, quarter” rhythm, asking the child to listen for the heart that has 2 sounds. Even young children can figure out it is the third heart. So he/she draws eighth notes in the block above the 3rd heart and quarter notes above the other hearts on that row. You can do the same rhythm again for the next 3 lines, or vary the eighth note pattern. You don’t want to have more than one beat with eighth notes at this point unless your student is older, but later on you can. If the student has trouble, break down the steps further and delay writing until the student is ready.
Tomorrow I will post a similar worksheet for two measure dictation.