Burnell's search for the Aindra school took him to Southern India where he came across the Tamil grammatical work Tolkappiyam.
A preface of this work, written during the twelfth century CE by Ilampuranar describes the work as aindiram nirainda Tolkappiyam[incorrect quote]('comprising Aindra').
Burnell posits that this is an allusion to the pre-Pāṇinian Aindra school of grammar.
While his demonstration of the influence of Sanskrit on the Tolkappiyam has met with some approval, his attribution and approximation of all non Pāṇinian schools of Sanskrit grammar with the Aindra school has met with resistance.
[1][2] Some scholars have also taken a less committal line on the question of Sanskrit influence itself.