The Trumpeter and the Echo Op. 89, No. 15 by Russian composer Dmitri Kabalevsky is a 20th Century work from his set called 35 Easy Pieces. It’s an Early Elementary work featuring Imitation and Melodic 4ths.
Stubborn Mule by American composer Frances Clark is a Modern era work from her method called The Music Tree. It’s a Primary work featuring Partial Staff Notation, Melodic 2nds and Blocked 2nds.