Past efforts invested in computer-based education technology interventions have generated little evidence of affordable success at scale. This paper presents the results of a mobile phone-based intervention conducted in the Indian states of Andhra Pradesh and Tamil Nadu in 2012-13. The BridgeIT project provided a pool of audio-visual learning materials organised in accordance with a system of syllabi pacing charts. Teachers of Standard 5 and 6 English and Science classes were notified of the availability of new videos via text messages (SMS), which they downloaded onto their phones using an open-source application and showed, with suggested activities, to students on a TV screen using a TV-out cable. In their evaluation of this project, the authors of this paper found that the test scores of children who experienced the intervention improved by 0.36 standard deviations in English and 0.98 standard deviations in Science in Andhra Pradesh, relative to students in similar classrooms who did not experience the intervention. Differences between treatment and control schools in Tamil Nadu were less marked. The intervention was also cost-effective, relative to other computer-based interventions. Based on these results, the authors argue that is possible to use mobile phones to produce a strong positive and statistically significant effect in terms of teaching and learning quality across a large number of classrooms in India at a lower cost per student than past computer-based interventions.