There were two exceptions. Trophimoi or "foster sons" were foreign students invited to study. The Athenian general Xenophon, for example, sent his two sons to Sparta as trophimoi. Also, the son of a helot could be enrolled as a syntrophos. . if a Spartiate formally adopted him and paid his way; if he did exceptionally well in training, he might be sponsored to become a Spartiate. Spartans who could not afford to pay the expenses of the agoge could lose their citizenship.
There were two exceptions Trophimoi or "foster sons" were foreign students invited to study The Athenian general Xenophon for example sent his two sons to Sparta as trophimoi Also the son of a helot could be enrolled as a syntrophos  if a Spartiate formally adopted him and paid his way; if he did exceptionally well in training he might be sponsored to become a Spartiate Spartans who could not afford to pay the expenses of the agoge could lose their citizenship