The school is a McDojo if the class mostly practices forms, one-step (self-defense or sparring), or board breaking

Now if the school has de-emphasized sparring, then they must be doing forms, one-step self-defense, one-step sparring, or break practice. You'll usually hear this as a complaint from street-fighters who assume a martial art is no good because they have forms and breaking. They don't understand the benefit of what forms can engender, and usually spout Bruce Lee's famous quote (which was made in the context of a movie, rather than in a memoir or instructional context), which is, "Boards don't fight back". The argument against board breaking is that it doesn't allow for proper sparring technique. And therein lies the problem. Nobody ever said that was the purpose of breaking. And so the complainer is correct - it doesn't help sparring.

What then, is the purpose of forms? Forms, whether you use the English term "form", "pattern", or "movement", or the Japanese "kata", or the Korean "poomsae", "tul", or "hyung", they all mean the same thing. They are a series of choreographed techniques. As the student advances in rank, the techniques in the form become more complex. Forms serve a multitude of purposes. They preserve the techniques for the art. It is analogous to a child who learns words easier when sung than when said. A child will learn the words to a song faster than the words of a poem. That's because there is an element of rhythm, fun, and repetition. With forms, the student can practice them in solitude. It is harder for a student to be told, "go home and practice a reverse punch, a front snap kick, a low block, and a forward stance". When they get home, they say to themselves, "ok... punch, front kick, stance... what was the other thing??"

With forms, the student has learned a pattern of movements that make it far easier to remember the instruction to go home and practice the punch, block, kick, and stance. In fact, a student learns a good many other things, as well: rhythm, breath control, turning, stepping, and combining techniques. Imagine an instructor giving this instruction to a student:

Go home and practice steping to left or right whilst performing a low block; performing a combination of low block and punch; using forward stances and walking stances in conjunction with high blocks and punches; your kihaps/kiai. And all the while, do them smoothly (or hard, or fast, or slow). Huh?

This is much simpler: "Go home and practice Taeguek 1".

What then, is the purpose of breaking? If boards don't hit back, why then, do we hit the boards? For one thing, it teaches the student about focus; follow through; control of technique; the effects of power and energy dispersion; and the physics of momentum, impulse, velocity, and mass. These can be learned in sparring to some degree. But the pace of sparring is such that this activity doesn't lend itself very well to learning these concepts, and so breaking is found to be a very effective tool instead.

Unless, of course, one denies the applicability of focus, follow through, control of technique, power, energy, momentum, impulse, velocity, and mass to sparring.

What then, is the purpose of "one steps"?  It builds a foundation on which we can apply sparring and self-defence techniques. When performing a one-step self-defence technique, one partner goes into a stance, like a step backward into a low block; while the other readies him or herself for an attack. The other partner then steps forward into a controlled punch toward the face. The defender chooses an appropriate defense. The attacker simulates being attacked by bending forward or twists or contorts in response to the imagined attack. And then they switch roles.

Yes, not very realistic, of course. This isn't what happens on the street - and it is on the street for which we practice these techniques. The critics complain this isn't realistic, because the sequences are executed too slowly. My response would be to inquire how can a defender perform a technique quickly if s/he can't perform them slowly? It is only through repetition that the slow technique can morph into a speedier execution on the street.

Critics will complain, "well, why don't the black belts do them at full speed?". And my answer is simply, "I don't know". Senior belts should be performing self-defense techniques are real-time speed - certainly dynamically. Static practice is fine when first learning the technique, but when the student begins to become comfortable with the tecnique, then they should be doing them faster.

Schools that don't do this are doing a disservice to their students, because the students are being sent into the world with a false sense of security that they can handle themselves. They could get killed or seriously injured if they are called to use their techniques.

In the end, there is nothing wrong with doing or not doing forms, one-steps, or breaking. A good school will balance them.  But a school that doesn't isn't necessarily a McDojo.

Some schools - notably Aikido - do not spar, compete, or break.  And their forms are their self-defense.  In this case, there are philosophical reasons not to spar, compete, or break.  That does not mean the school has bad instruction.