Thailand is beginning to emphasize the teaching of elementary, junior and senior high students to speak English. One of the key problems has been the availability of an effective English learning program. This research study evaluated the effects of a mobile English speaking software app (Qooc o Kids English) for two schools using mobile devices in which 95% of the phones were Android, The research questions’ focus was on English speaking ability. Qooco Kids English is an online program delivered via a mobile device. The Qooco Kids English App w as used to teach children to speak English fluently by providing English audio models and frequent speaking practice with immediate actionable feedback on the English speaking of the students. Qooco Kids English has twelve instant feedback lesson modules w ith gamified, progressive lessons which result in faster and more engaging learning lessons. Through a pre post experimental design, the researchers studied the speaking ability of 192 grade 5 and grade 6 students in Chiang Rai Municipality School 6 and 89 Junior and senior high students in Chiang Rai Municipality School 7 for one semester in Thailand. Specifically, effects on students' English speaking ability after one semester were measured through the iTest pre and post tests. The significant statistic al findings indicated that the Qooco software English speaking app increases student achievement in both spoken and written English for Grades 5 and 6 as well as junior and senior high school students.