Errors indicate learners' misunderstanding and can provide learning opportunities. Providing learning support which is contingent on learners' needs when errors occur is considered effective for developing learners' understanding. The current investigation examines how tutors and tutees interact productively with errors when working on a mathematical word problem. Many learners have difficulties with solving word problems. Teachers are challenged to support the learners in solving word problems, especially when errors occur, in a way that enables them to solve future word problems independently. In this investigation, we analyze 26 teacher-student interactions regarding the occurrence of errors and contingent learning support. We pursue three research questions: first, which types of errors occur when students work on an algebraic word problem? Second, which types of contingency can be found during and after the tutors and tutees deal with the errors? Third, is there a significant relationship between the types of errors, contingency, and students' performance in the transfer task? Our results show that, first, misinterpretation of text is the most frequent type of error. Second, tutors in successful tutoring situations mainly instructed their tutees both during and after they help the tutees with their errors. Third, students' performance in the transfer task is significantly related to the contingency used during errors. In successful tutoring situations, when tutors support the tutees contingently, they do so mainly by instruction, whereas in unsuccessful tutoring situations, contingent support varies. Thus, contingency does not seem to be sufficient to promote learners' understanding. Further analyses are needed to clarify the role of instructional guidance when errors occur.