What kinds of interventions are most effective for these schools? Teacher shortage and disciplinary climate are inter-related: most teachers tend to avoid schools with more disciplinary problems, while a shortage of qualified teachers adversely affects disciplinary climate. What is needed in these schools is an intervention to break this vicious cycle. Countries that have improved their performance in PISA, like Brazil, Colombia, Estonia, Israel, japan and Poland, for example, have established policies to improve the quality of their teaching staff by either adding to the requirements to earn a teaching license, providing incentives for high-achieving students to enter the profession, increasing salaries to make the profession more attractive and to retain more teachers, or by offering incentives for teachers to engage in in-service teacher-training programmes.