Around 1886, there was a sudden growth in population, due to the completion of the railway. Mr Felix Thistlethwayte was the Principal at this time and enrolment at the school was over 200. Mr Thistlethwayte decided the school should be organised into two departments - Boys and Girls – not the more usual Infants and Primary. He felt this division would render the school population more manageable as they would be of approximately equal size and that a female teacher would best suit female students, thus securing a larger and more regular attendance. The girls' department was established in 1889.
The school numbers continued to grow and, in 1913, Acting Chief Inspector McLelland reported that there were 400 children enrolled in the Infants Department but only 280 seats. In the Primary Department, three girls were sitting in each dual desk and eight or nine boys were crowded into a long nine foot desk. This marked the next step in the Hurstville Public School expansion that still continues today.