Now, I am not sure about doctors- whether the normal apprentice system would apply to them. But for trades there would be two kinds of apprenticeships: voluntary and involuntary. For the first, the indenture contract would indicate that the apprentice was signing freely.. Apprentices agreed to be obedient, attentive to their tasks, not get drunk, stay away from playhouses, not marry, not steal form the shop or steal the master's property. The master agreed to feed, house, clothe, teach the "art and mystery" ( skill and knowledge) of the craft, and often set aside time for schooling. Given we're talking about teenagers, mostly, there are plenty of examples of these agreements being broken; accounts of apprentices taking off in the middle of the night and raising hell in town, getting a girl pregnant, running with scissors, etc. And, because businessmen are sometimes greedy and penurious, there are examples of masters definitely not living up to their bargains, either: like the Boston rope-maker who set his apprentice out on the rope walk on a cold January day and froze him to death. If bad enough, these breaches of contract could make their way into court, like James Jamison, apprenticed to Henry Broughton but released by the New York court in 1718 after showing his face so disfigured from violent beatings that he was in danger of going blind.

Parents played a big part. In those lists of agreements, you can see the hand of the apprentice's family, bargaining. How successful they were depended on the economy. In Pennsylvania of 1770, like in most of the colonies, there would be great demand for apprentices, and labor in general. There, a good bargain might be struck with a master. On the other hand, in Geneva around the same time, watchmakers were so besieged with parents trying to get their children into the trade that they expected to be paid for the privilege of taking them. Joseph Moxon in 1683 published a guide to the skilled trades so that parents wouldn't mistakenly push their child into the wrong one. But things did not always work out, anyway. Apprentices not uncommonly thought better of their situation and ran ( Ben Franklin being one example). As they were bonded, not free, the master could put an ad in the paper with a reward for the apprentice's capture. Some of these ads are perhaps not asking for their return. The New York printer whose ad described the runaway as bloated by heavy drinking "to which he is most uncommonly addicted " might not have been asking for him back, instead just giving legal notice that the contract between them was now null and void. But there was a time aspect to the economics of runaways: in the first few months, an apprentice would likely be just doing a lot of sweeping and watching. If he ( though sometimes girls were apprenticed, most were male) ran off, it was not a great loss to the master. On the other hand, if as usual he was indentured for seven years, at the end of four or five he'd be very useful and skilled: and working for his master for free. He might decide to run off with his skills- and then the master might well offer a reward to get him and his skills back.

With the voluntary, there was also the involuntary indenture. The courts always had a certain number of orphans and abandoned illegitimate children to manage, and forced indentures were a common way of moving them along. Unlike the careful parents striving for a good deal, the courts often didn't seem to care too much about the details. When John Dunlap apprenticed himself for five years to William Jackson in 1698, to learn shoemaking , he was to get two suits of clothes at the end of his term ( one suit of which was to be nice enough to be worn on Sunday) and he had set times for schooling. A few years later, Jackson was approached by church and town authorities to take on John Reade, an orphan of eight. Reade was signed on for twelve years, not five. And though there was mention of teaching him to read and write, and giving him the "usual provisions", no mention was made of him having set times for school or getting nice clothes at the end. He disappears from the record with his indenture: perhaps he didn't live to twenty. Twelve years, perhaps in rags...you can almost see him with a bowl, asking, "please, may I have some more?"

Simon Middleton From Privileges to Rights: Work and Politics in Colonial New York

Bridenbaugh: The Colonial Craftsman