This is a very important question. This is because Theravadin Buddhism has quite a number of requirements which are necessary before you take a Bodhisattva vow. And these requirements are very high. It is written in the Theravada scriptures that some of the requirements to take a Bodhisattva vow are that you have to be born during the lifetime of a Buddha, you have to take that vow in front of a living Buddha, and the Buddha has to perceive that you have the capacity to achieve such a vow. So, as the Buddha of this era died over 2500 years ago, according to Theravadin Buddhism, no one can actually have those requirements at this time. Another requirement to take a Bodhisattva vow is that one has to have the capacity in that lifetime to become fully enlightened. So one has to have the Perfections necessary to become an Arahant during the lifetime of a Buddha. More requirements necessary is that one has to already be an ascetic, that is, one who has left the home life and is in search of the truth, as well, have already attained all the psychic powers.
Theravada Buddhism does have the Bodhisattva vow, however the requirements for taking one means that you have to be very, very highly evolved.
I was once talking to a Thai person and we were taking about Compassion for ourselves and Compassion for others. She recognized that I had some leanings towards being a Bodhisattva. She said: "Well I hope that you will become a Bodhisattva". She didn't think that I could become a Bodhisattva in this lifetime. Because in Theravada Buddhism, to take on a Bodhisattva vow and become a Buddha is considered to be a very high vow. However, in Thailand they have the term "Muan Phra Bodhisat": like a Bodhisattva. That is, you practice in this lifetime like a Bodhisattva, so that you can increase the qualities of your Paramis so that if you are born in the lifetime of a living Buddha, then you may actually be inspired by the presence of a Buddha and have all these requirements necessary to take on that vow. In Theravadin Buddhism it is realized that in order for the Buddha's teachings to go down through the centuries we need the Noble Sangha, enlightened disciples. We can't all be the captain of the ship, we also need the crew. For the teachings to continue down through the centuries after the Buddha, it is necessary to have other people becoming fully enlightened under his teachings.
Now also according to Theravadin teachings on Bodhisattvas, a Bodhisattva cannot be enlightened with the teachings of another Buddha. If you are a Bodhisattva, you haven't yet reached any level of enlightenment. This is just the definition: that you must not have reached any level of enlightenment. In Theravadin Buddhism, there are four levels of enlightenment: stream enterer, once-returner, non-returner and full enlightened, an Arahant. According to the scriptures, once you are at the first level of enlightenment, there are only seven more lifetimes, at most, before you become fully enlightened.
So in order to become a Bodhisattva you have to postpone your personal enlightenment. If you are working towards becoming a Bodhisattva you can, in Theravadin Buddhism or in Thai Buddhism, practice "Muan Phra Bodhisattva - like a Bodhisattva)" until your Paramis are sufficient enough that you are born in the lifetime of a Buddha and have all these requirements necessary to take on this higher vow. Perfecting the Paramis over lifetimes and lifetimes is not such an easy thing to do, and it would be helpful for people to understand this.