Wikipedia has an article,
Studies of Waldorf education,
which cites various publications, not, however, specifically focused on mathematics education.
[Not the same Wikipedia article to which @JoelReyesNoche refers.]
(1) A 2012 study compared the reading and math standardized test scores obtained in public Waldorf schools in the United States with scores for their districts as a whole, as well as scores in matched comparison schools. Public Waldorf school scores were lower than those of regular public schools in earlier grades (second and third), but higher in seventh and eighth grade.
Abigail L. Larrison; Alan J. Daly; Carol VanVooren (October 5, 2012). "Twenty Years and Counting: A Look at Waldorf in the Public Sector Using Online Sources". Current Issues in Education. 15 (3).
Another reference from the same Wikipedia article:
(2) A 2009 PISA study found that, compared to state school students, European Waldorf students are significantly more capable in the sciences, slightly less capable in mathematics; and comparable in reading ability.
(PISA = Programme for International Student Assessment)
And here is statement from a particular US Waldorf school:
(3) WSL’s math curriculum largely mirrors the Massachusetts state standards; however, the range of teaching techniques is broader.