LONDON — He reads fluently (while wearing a Gruffalo costume), he does math with ease and he can explain scientific concepts such as how rain forms.

He is also 3 years old.

The toddler, Muhammad Haryz Nadzim, was invited last week to join Mensa, a British society whose membership rules require an I.Q. in the top 2 percent of the population.

Haryz, as his family calls him, received an invitation to the society after meeting with a consultant psychologist who assigned him a score of 142 using the Stanford-Binet intelligence test. Scoring above 145 is considered “genius or near genius,” according to the test’s website.

The 3-year-old is now Mensa’s youngest current member, the society said in an email on Wednesday. The youngest-ever member was age 2 years 4 months at the time of joining.