What educational researchers say
Maths Anxiety can be described as “the panic, helplessness, paralysis and mental disorganization that arises among some people when they are required to solve a mathematics problem” (Tobias & Weissbrod, 1980). https://www.sheffield.ac.uk/polopoly_fs/1.753619!/file/Maths_anxiety_strategies.pdf
Christie Blazer says "A number of researchers have hypothesized that math anxiety disrupts performance because it reduces students’ working memory, leaving them unable to block out distractions and irrelevant information or to retain information while working on tasks (Sparks, 2011; Legg & Locker, 2009; Ashcraft & Krause, 2007; Cavanaugh, 2007; Beilock & Carr, 2005). https://files.eric.ed.gov/fulltext/ED536509.pdf ... I would add that often low attaining learners already have smaller working memories so for them this is an even larger problem to overcome.
Gerardo Romirez: Motivated Forgetting in Early Mathematics. "Educators assume that students are motivated to retain what they are taught. Yet, students commonly report that they forget most of what they learn, especially in mathematics ... this proof-of-concept study suggests that children may deal with threatening classroom experiences by forgetting important course relevant knowledge."
timely practice says
Often low attaining learners already have smaller working memories so for them a reduction in working memory is an even larger problem to overcome.