This research is an extension of a large-scale survey on new-immigrant children conducted by the National Academy for Educational Research in 2012. This research chooses a representative subsample from the existing sample of new-immigrant children from northern Taiwan for continued tracking of their mathematics progress and influencing factors. After removing transfer students, 630 students (71.11% of the total) were willing to take the test and 626 (70.65%) were actually tested, with an average age of 12.36. Research tools employed include a mathematics achievement test, a student questionnaire, a learning program questionnaire for new-immigrant children, and a perspective questionnaire for school contacts. The questions used for the mathematics achievement test are multiple choice questions selected from the Taiwan Assessment of Student Achievement item bank. A total of 78 questions were arranged into 13 booklets using the method of balanced incomplete block design. Each booklet contained 24 questions, meaning each student needed to answer 24 questions in 40 minutes. Cronbach’s alpha was shown to be between .82 and .90 for each booklet. The student questionnaire included 24 background information items and 26 psychological construct items. The standard error was estimated using the Jackknife method, and the growth rate as well as the interaction between growth rate and relevant key influence factors were estimated using a many-faceted Rasch model. The software used was Acer ConQuest 3. In general, new-immigrant children’s progress in mathematics performance is 0.479 logit per year, which is not far from international results. Comparison of the 2012 and 2014 test results on four mathematical topics, namely, “numbers and measurement,” “geometry,” “statistics and probability,” and “algebra,” indicate that “geometry” has the worst pass rate for new-immigrant children. Besides, remedial instruction is unable to provide new-immigrant children with lower performance with a chance to catch up, although it does provide them with progress matching their peers. The new-immigrant children who are well adapted to classroom rules have a significantly higher growth rate for mathematics performance than those who do not adapt well to classroom rules. Based on the research findings, this research proposes detailed suggestions with regard to the intended curriculum, remedial instruction project, and practical helping for new-immigrant family.