Learn Hardcore Spanish (Latin America): La vendedora me dejó entrar al probador y comprobó que mi talla es mediana. - The saleswoman let me enter the fitting room and checked that my size is medium.

dejar + [person] + infinitive: La vendedora me dejó entrar.
You can also attach the clitic to the infinitive: La vendedora dejó entrarme (less common but correct).
A more formal alternative is permitir: La vendedora me permitió entrar.
Another equivalent structure is dejar que + subjunctive, but then you don’t use the object pronoun: La vendedora dejó que (yo) entrara. Avoid “me dejó que entrara.”

Tip: dejar de + infinitive means “to stop doing” (e.g., dejó de fumar), which is unrelated here.

Why is it "entrar al probador" and not "entrar en el probador"?

In Latin America, entrar a is very common, and a + el contracts to al. In Spain, entrar en is more common. All of these are correct:

entrar al probador (LatAm preference)
entrar en el probador (Spain preference)
entrar a el probador is incorrect because you must contract to al.

What exactly is a "probador"? Are there regional alternatives?

Probador is a fitting/changing room in a clothing store. Common alternatives in Latin America:

vestidor (also very common on store signage)
Less commonly for stores, camerino tends to be a backstage dressing room. You’ll see signs saying Probadores or Vestidores.

Why do "dejó" and "comprobó" have accent marks?

They’re third-person singular preterite forms and are stressed on the last syllable:

dejó (from dejar)
comprobó (from comprobar) The accent marks indicate the correct stress and distinguish them from present-tense forms like deja and comprueba.

Why use the preterite (dejó, comprobó) here instead of the imperfect?

The preterite presents completed events with clear boundaries: she allowed you in (done) and confirmed your size (done). The imperfect (dejaba, comprobaba) would describe ongoing, habitual, or background actions, which doesn’t fit this one-time sequence.

Why does it say "comprobó que mi talla es mediana" (present "es") after a past verb? Would "era" also work?

Both are possible:

…comprobó que mi talla es mediana: emphasizes that the result is still valid now.
…comprobó que mi talla era mediana: frames it within the past context. With comprobar (“to confirm/verify”), the subordinate clause usually takes the indicative, not the subjunctive, because it asserts a fact.

Why "mediana" and not "mediano" or "medio"?

Because talla is feminine, the adjective agrees: talla mediana.

mediano/mediana = medium-sized.
medio usually means “half” or functions as an adverb (“kind of”), not a clothing size.

What’s the difference between "talla", "tamaño", and "número"?

talla: clothing size (shirts, pants, jackets).
número: shoe size (and sometimes rings).
tamaño: general size of things (boxes, rooms) or of a body part in a non-sizing-chart sense.

Other natural ways to say "my size is medium"?

Uso/tengo talla M (said “eme”).
Uso/tengo talla mediana.
Soy talla M/mediana (informal).
On labels you’ll see S, M, L; you can also say pequeña, mediana, grande.

Is "comprobar" the same as "probar" or "probarse"?

No:

comprobar = to check/confirm/verify a fact (e.g., comprobar que la talla es mediana).
probar = to try/taste/test.
probarse = to try on clothing (reflexive), e.g., me probé la camisa.

Could I replace "comprobó" with other verbs like "verificó", "confirmó", "revisó", or "chequeó/checó"?

Yes, with nuances:

verificó / confirmó: close to comprobó (formal/neutral).
revisó: “looked over/checked,” not always implying confirmation of a fact.
chequeó (many countries) / chequeó/chequeó vs checó/checó (Mexico often says checar/checó): informal/colloquial “checked.”

Is "me" a direct or indirect object here? What would it be in third person?

With dejar + infinitive, the person is typically the direct object. For 1st/2nd person, the form me/te/nos/os doesn’t show the difference. In third person:

Standard in Latin America: La vendedora lo/la dejó entrar.
In Spain, leísmo is common and accepted: La vendedora le dejó entrar (masculine human referent).

Can the clitic go on the infinitive: "dejó entrarme al probador"?

Yes. Both are correct:

Me dejó entrar al probador (more common).
Dejó entrarme al probador (also fine).

Why not "me dejó que entrar"?

Because with dejar que, you must use the subjunctive without the clitic object:

Correct: Dejó que (yo) entrara.
Correct: Me dejó entrar.
Incorrect: Me dejó que entrar.

Is "comprobó de que" ever correct?

No. That’s dequeísmo. Use:

comprobar que (no “de”): comprobó que mi talla es mediana. But some verbs do take de que, e.g., asegurarse de que: Se aseguró de que todo estuviera listo.

Why "ser" (es) and not "estar" with "talla"?

Size as an inherent attribute uses ser: Mi talla es mediana. You use estar/quedar for fit in the moment:

Esta camisa me queda grande/chica.
Not: “Mi talla está mediana.”

Could it be "un probador" instead of "al probador"?

Yes, but it changes the meaning:

al probador = to the (specific) fitting room.
a un probador = to a fitting room (unspecified/one of them).

What does "vendedora" imply? Are there other words?

Vendedora is a female salesperson. Alternatives:

vendedor (male), vendedora (female).
dependiente/a (common in Spain).
empleado/a (employee; generic).
cajero/a (cashier), a different role.

Any quick pronunciation tips for tricky parts?

talla: the ll is usually pronounced like English “y” (TA-ya) in most of Latin America.
v is pronounced like b: vendedora ≈ “bendedora.”
Accented forms dejó, comprobó stress the last syllable.