 While in the US, Ostrovsky earned his living teaching a wide variety of subjects, including Hebrew, history, Bible, as well as Yiddish.He became a renowned and respected educational figure, as director and inspector of schools as well as principal of the teacher's seminary of the Workmen's Circle Jewish educational system.Contemporaneously with his educational work, Ostrovsky was active in the Zionist Movement's labor organization, Poale Zion, with the leaders David Ben-Gurion, Ber Borochov and Yitzhak Ben-Zvi.