From what I can tell, Jo's work is based on how low socio-economic-status (poor black / latino) students have trouble in standardized exams when there are questions like:
"A cable crew had 120 feet of cable left on a 1000-foot spool after wiring 4 identical new homes. If the spool was full before the homes were wired, which equation could be used to find the length of cable (x) used in each home?".