In the Central and Northern India, people used the bark of the tuz tree - say one yard long and as broad as the outstretched fingers of the hand. The 'prepared' bark was used for writing. The whole book is wrapped up in a piece of cloth and fastened between two tablets of the same size. Such a book is called puthi (cf. pusta, pustaka).
In two places [to my knowledge] in the works of Kavi Kalidasa there are references to Pustakam or palm leaf as a writing material. In Syamaladandakam - '.. . . . पुस्तकं चापरॆणांकुशम्’. ’हस्ते किं ते? ताली पत्रम्’.
I wonder what type of Pustakam Kavi Kaladasa refers to in the Syamaladandakam. Was palm leaf being used by school-going children during Kalidasa's period for writing?
Scholars may throw some light on this.
Respectful regards.
R Subrahmanian