Take an Arduino or Teensy prototype to Mass production - Loading software onto microcontroller I am developing an educational product that I would like to mass produce. I am not sure of the quantity yet, but I imagine we will make a few hundred PCBs at least to begin

I spoke with an electrical engineering about how to take an Arduino prototype to mass production, and he warned me that the code written in the Arduino IDE cannot be fused onto the processor. (He used the term "fuse", although I don't see this elsewhere in the forum. is this the right term?)

He said that I would probably have to take each product, and load the Arduino code on manually, plugging in each one to a computer and upload like one would when prototyping. Also, he said the other option would be to recode my Arduino sketch from scratch using an AVR code.

Can someone shed some light on this for me? How can I take Arduino prototyping code and use it in mass production?
Arduino code and AVR code is essentially the same, at least once compiled it is. The only real difference is the existence of the bootloader, and that is not essential.

For quantities of a hundred or so it is probably most cost effective to manually program them via an ISP connector to the board. For larger quantities Atmel provide a mass programming service to pre-program the chips, but that costs money so the more you have done at once the cheaper it is per chip. I am not sure on Atmel's procedure off hand but others I have used just take either a .elf or .hex file which the Arduino IDE is perfectly capable of producing.

Either way you should design in an ISP connector on your board so the firmware can be upgraded in the future if needed.