A meditation teacher I once had said that access concentration (the stage before the jhanas) is the same level of concentration that one has when reading a good book or when fully engaged in conversation. However when I've read about it in other places it makes it seem like it is a more special level of concentration, perhaps one that you wouldn't ordinarily experience in your day to day life. Which point of view is more correct? How concentrated is access concentration and how would one recognise it?
The Visuddhimmagga defines upacāra samadhi in IV 32-34:
Now concentration is of two kinds [access and absorption]. [...] The difference between the two kinds of concentration is this. The factors are not strong in access. [...] just as when a young child is lifted up and stood on its feet , it repeatedly falls down on the ground. [...] The arousing of the counterpart sign, which arises together with access concentration, is very difficult.
The process of concentration as described in the Abhidhammattha Sangaha (IX 17, 18):
When that sign has been throughly aprehended and enters into range of the mind door just as if it were seen by the eye, then it is called the learning sign, and that meditation becomes concentrated. When one is thus concentrated, one then applies oneself to meditation by means of that preliminary [parikamma] concentration based on the learning sign. As one does so, an object which is the counterpart of that (learning sign) becomes well established and fixed in the mind -- (an object) which is freed of the flaws of the original object, reckoned as a concept, born of meditation. Then it is said that the counterpart sign has arisen.
Thereafter, access [upacāra] development is accomplished, consisting in concentration of the sense sphere in which the obstacles have been abandoned.
Fast forward to our current century:
Access concentration is characterized by the significant reduction or complete dropping of the five hindrances and the arising and strengthening of jhāna factors. [...] It is easy to confuse momentary concentration with access concentration. One difference is that with access concentration, the meditator's continuity with the object is much longer and more stable over time. Another difference is that with access concentration, the object is much more energized and "bright". [...] In access concentration, the jhāna factors are present but insufficiently strong for full absorption into jhāna.
-- Stephen Snyder & Tina Rasmussen (Practicing the Jhānas)
or more broadly speaking:
The Buddhist tradition has introduced the term upacāra samadhi [...] to refer to a non absorptive experience of concentration that begins with the arising of the counterpart sign and endures until consciousness enters into full absorption. Upacāra samadhi implies concentration that is in the vicinity of jhāna [...] and describes the experiences that precede absorption, but it does not necessarily leads to jhāna. It may refer to the conditions that precede jhāna; it may refer to experiences that are reminiscent of first jhāna mental factors, but without the seclusion of absorption; and it may describe the mature concentration that accompanies those meditation objects (such as discernment of the body parts, and various recollections) that do not have the potential to reach full absorption. [...] Some meditators use the term upacāra samādhi so loosely that it merely describes the feeling of being concentrated and a mind that is stable and happy during meditation.
-- Shaila Catherine (Wisdom Wide and Deep)
A meditation teacher I once had said that access concentration (the stage before the jhanas) is the same level of concentration that one has when reading a good book or when fully engaged in conversation.
No it's not. Reading a book or engaged in conversation lacks Ekagatta or One Pointed Concentration which is one of the Five Factors of Jhana. Access Concentration means all Five Jhana Factors are present but are not strong enough. The mind is calmed when the body is calmed. So you can't be talking or moving around. Mind and body must be calmed. It's not the same thing. You can be absorbed in anything but it's a different thing to be absorbed in Jhana. Because the five factors must be present. And it's not dependent on the five senses. So it's nothing we've experienced before.